In recent years, great attention is directed to hybrid vehicles from the standpoint of environmental problems. A hybrid vehicle has a plurality of power sources incorporated. A hybrid vehicle incorporating, as the driving source, a power storage device (battery, capacitor and the like) and a motor, in addition to a conventional engine, is already put into practical use.
A fuel cell car incorporating a fuel cell for the power source is also attracting attention. In a broad sense, a vehicle incorporating a power storage device such as a battery and capacitor, in addition to a fuel cell, as the power supply, can be taken as a hybrid vehicle incorporating a plurality of power sources.
There is also known a hybrid vehicle with an external charging capability for charging a power storage device by means of an external power supply. Such a hybrid vehicle with an external charging capability is advantageous in that the frequency in stopping over at a resupply stand for the supply of fuel will be reduced if the power storage device can be charged from, for example, a commercial household power supply.
Japanese Patent Laying-Open No 2007-62639 (Patent Literature 1) discloses a hybrid vehicle that can force a power source reduced in operation frequency to operate. This hybrid vehicle includes, as the power source, an engine, as well as a power storage device and a motor generator. When the HV mode transition switch is turned on during the run of an EV mode in which the vehicle runs with only the power storage device and motor generator as the power source, the control device shifts the running mode to the HV mode in which the vehicle runs with also the engine driven.    Patent Literature 1: Japanese Patent Laying-Open No. 2007-62639